A self-tightening drill chuck such as described in German patent document DE 10 2005 018 392 published 26 Oct. 2006 has a chuck body centered on and normally also rotatable about an axis, a tightening sleeve that can be rotated coaxially on the chuck body and is axially supported on a jaw holder that is mounted on the chuck body and in which jaws are slidable in guide slots. The jaws can slide radially and axially for clamping and releasing by means of the jaw holder by a relative rotation between the chuck body and the tightening sleeve. The drill chuck also has a latch having a ring of teeth coaxial with the chuck axis, and a pawl mounted on the jaw holder and engageable with the ring gear under the force of a spring. The latch prevents the chuck body and the sleeve from undergoing relative rotation and releasing the jaws when the pawl is engaged with the ring gear, but does not hinder relative rotation for tightening the chuck.
A stop is provided on the jaw holder and a counterstop is provided on the tightening sleeve to define end positions for the relative rotation of the tightening sleeve with to the jaw holder. One end position corresponds to the engaged position of the pawl, and the other end position to the disengaged or freeing position thereof. A retainer device has seats associated with the two end positions and is mounted between the jaw holder and the tightening sleeve. This retainer only allows rotation of the tightening sleeve with respect to the jaw holder, at least in the rotational direction of the tightening sleeve corresponding to the clamping, once a predetermined clamping force has been attained.
Thus the chuck is tightened by rotating the sleeve in the tightening direction. This action shifts the sleeve, if necessary, into one end position and thereby causes it to rotationally entrain the jaw holder and jaws, moving these jaws radially inward and axially forward until they seat solidly on, for example, a tool. During this action the pawl ratchets on the sawteeth. The retainer holds the system in this position during the drilling operation and the angling of the teeth and pawl prevents the chuck from loosening. Normally also the structure is set that the forces in the chuck tend to tighten it during drilling, whence the self-tightening feature.
For loosening the chuck the sleeve is twisted in the loosening direction with enough force to free it from the spring force of the retainer and return it to the opposite end position, in which a cam formation on the sleeve tips the pawl into the freeing position. Further rotation of the sleeve in the loosening direction thus rotationally entrains the jaw holder and shifts the jaws axially backward and radially outward, and once this process is complete the retainer holds the chuck in this position until a new bit or the like needs to be chucked.